1. Field of the Invention
The present invention relates to a manufacturing method of a piezoelectric vibrating piece, the piezoelectric vibrating piece, a piezoelectric vibrator, an oscillator, an electronic equipment and a radio-controlled timepiece.
2. Description of the Related Arts
In recent years, in a portable telephone and a portable information terminal equipment, there is used the piezoelectric vibrator utilizing a quartz crystal or the like as a time instant source, a timing source of a control signal, a reference signal source, and the like. As to this kind of piezoelectric vibrator, although various ones are provided, as one of them there is known a surface mount type piezoelectric vibrator constituted by a piezoelectric vibrator plate in which the piezoelectric vibrating piece has been formed by being surrounded by a frame-like part, and a lid member and a base member, which have been anode-bonded above and below so as to nip the piezoelectric vibrator plate between them.
Especially, in recent years, there is provided a grooved piezoelectric vibrator whose equivalent resistance value has been suppressed to a lower value (See, e.g., WO 00/44092).
This piezoelectric vibrator possesses a piezoelectric vibrator plate comprising a piezoelectric vibrating piece, which consists of two vibrating arm parts extending parallel, and a frame-like part fixing a base end side of the piezoelectric vibrating piece, and groove parts along a longitudinal direction of the vibrating arm parts are formed respectively in base end side upper/lower faces of the two vibrating arm parts.
Concretely, there is explained while referring to FIG. 21 to FIG. 23. FIG. 21 is a sectional view of one pair of vibrating arm parts having a conventional groove part. FIG. 22 is a process view in a case where an exciting electrode is formed on the vibrating arm part shown in FIG. 21, and a view showing a state in which a photoresist film having been coated around the vibrating arm part is being exposed by irradiating a parallel light from just above through an opening part of a mask. FIG. 23 is a process view in a case where the exciting electrode is formed on the vibrating arm part shown in FIG. 21, and a view showing a state in which the photoresist film having been exposed in FIG. 22 has been developed.
As shown in FIG. 21, the base end sides of two vibrating arm parts 120 are formed so as to become respectively an H type in section by a groove part 121. And, in a surface of each vibrating arm part 120, there are formed exciting electrodes 122, 123 whose polarities differ, and the two vibrating arm parts 120 are vibrated (bend-vibrated) in a predetermined period so as to mutually approach or separate.
Especially, in a case where the groove part 121 is formed in the vibrating arm part 120, since the two exciting electrodes 122, 123, which have been formed in regions on a side face of the vibrating arm part 120 and a side face of the groove part 121, become an opposed positional relation, an electric field is liable to act more efficiently in comparison with a case where the groove part 121 is not formed. For this reason, as mentioned above, a vibration loss is low and it is possible to suppress the equivalent resistance value as low as possible, so that there is suitably used for the piezoelectric vibrator in which a high efficiency performance is demanded.
Incidentally, the exciting electrode 122 (123) having been formed in a region on a bottom face of the groove part 121 does not become a positional relation opposed to the other exciting electrode 123 (122) having been formed in a region on a side face of the vibrating arm part 120, it is difficult to effect on the electric field, so that it does not become an electrode of such a degree as to effect on a characteristic.
Here, there is explained about formation processes of the two exciting electrodes 122, 123.
First, as shown in FIG. 22, to a whole surface of the vibrating arm part 120, there is coated a metal film 124 of chromium, aluminum or the like, which becomes the exciting electrodes 122, 123 later, and a positive type photoresist 125 for instance is coated on the metal film 124 by a spray coat and the like. Subsequently, a photomask 127 in which an opening part 126 of a predetermined size has been formed is located on the photoresist film 125. On this occasion, the photomask 127 is precisely positioned such that the opening parts 126 are located respectively on the vibrating arm parts 120 having nipped the groove part 121. Subsequently, a parallel light R is irradiated from above toward straightly just below, and the photoresist 125 is exposed through the opening part 126. On this occasion, the photoresist film 125 becomes a state having been exposed only in a region in which the opening part 126 has been formed.
Subsequently, after the photomask 127 has been removed, a development of the photoresist film 125 is performed. By this, since the photoresist film 125 is the positive type, it becomes a state in which only the region having been exposed has been removed as shown in FIG. 23. And, by etching-working the metal film 124 with this photoresist film 125 being made a mask and thereafter removing the photoresist film 125, the two exciting electrodes 122 and 123 whose polarities differ can be formed on an outer surface of the vibrating arm part 120 as shown in FIG. 21.
However, in the above conventional method, following problems are left.
That is, in order to cope with a miniaturization and an increase in efficiency of the recent electronic equipment or the like, an additional miniaturization and an additional increase in efficiency are demanded also for a grooved piezoelectric vibrator itself. In order to cope with this, it is considered to thin as much as possible a width W1 of each of left-and-right side walls nipping the groove part 121 as shown in FIG. 21. By doing so, it is possible to shorten a distance between the opposed two exciting electrodes 122, 123, and an electric field efficiency can be improved. Therefore, the additional miniaturization and the additional increase in efficiency can be intended, so that it is possible to respond to the above-mentioned needs.
However, the more the width W1 of the side wall is thinned, there arises a problem that it becomes difficult to divide the metal film 124 by the above-mentioned exposure process and development process to thereby electrically cut off the two electrodes 122, 123 respectively. That is, this is because, since it is impossible to narrow a division electrode width W2 (e.g., 10 μm) more than this in order to electrically, certainly cut off the two exciting electrodes 122, 123, if the width W1 of the side wall is thinned, a region for forming the division electrode width W2 becomes gradually null. For this reason, in a case where the width W1 of the side wall has become narrow, it is technically difficult to expose the photoresist film 125 such that the division electrode width W2 is certainly ensured, so that it has been impossible to form the two exciting electrodes 122, 123 under the state having been electrically, certainly cut off on the vibrating arm parts 120 having nipped the groove part 121. As a result, it has been difficult to respond to the above-mentioned needs.